This invention concerns a method of forming structures on a substrate using a high-temperature additive process, and in particular on a single-crystal superalloy substrate using a powder fed or wire fed laser deposition process.
Components of gas turbine engines such as combustors and turbine blades are commonly manufactured from nickel or cobalt based superalloys.
The superalloys are creep resistant at high temperatures but their characteristics make them prone to cracking on welding, or the welds may be brittle during service.
Superalloy structures are conventionally cast but may be formed through direct metal deposition. Direct metal deposition and other additive manufacturing techniques are high temperature processes that use multiple passes to deposit sequential layers onto a substrate. Each layer may have the same or different footprint to the other layers. In this way complex structures can be developed.
During the deposition process a laser or electron beam or such like is moved relative to the substrate and is directed at the substrate to create a traversing melt pool. Material, either in powder or wire form, is deposited into the melt pool and melted. As the melt pool traverses away from the deposition location the material solidifies to form part of a layer of the structure. Subsequent deposition can be used to deposit further layers on the first layer. Once the structure is complete it may be machined to remove excess material and to provide a structure to a higher tolerance than may be achievable by the direct metal deposition alone.
The melt pool in the substrate can be a source of flaws and of adverse microstructure. For substrates of a superalloy, particularly alloys of a single-crystal form, these created flaws and adverse microstructures are further undesirable as they can be a source cracks with the fatigue life of the component being impaired.